Device and method for controlling tilt servo

ABSTRACT

A tilt servo control device of an apparatus for recording information on and reproducing information from an optical recording medium set in the apparatus, the apparatus comprising an optical system for leading a laser beam emitted from a light source to a recording surface of the optical recording medium and a laser beam reflected by the recording surface of the recording medium to a photo detector and a read signal generator for generating a read signal in accordance with an output signal of the photo detector. The tilt servo control device determines a type of the optical recording medium, generates a tilt drive signal so as to reduce a tilt angle at a position of the laser beam irradiating the recording surface and an optical axis of the laser beam by a method for generating a tilt drive signal corresponding to the recording medium type, and drives a tilt angle adjuster for adjusting the tilt angle in accordance with the tilt drive signal.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a tilt servo control device anda tilt servo control method for compensating the tilt angle of arecording surface of an optical recording medium as defined by the anglebetween the normal to the recording surface of the recording medium andthe optical axis of a light beam irradiating the recording surface.

[0003] 2. Description of the Related Background Art

[0004] In order to correctly read information recorded on an opticaldisk such as a DVD (Digital Versatile Disk), it is necessary toirradiate a reading light beam perpendicularly relative to a recordingsurface of the optical disk. If the optical disk has a warp, or errorsin the mechanical system are large, it is impossible to irradiate thereading light beam perpendicular to the recording surface of the opticaldisk, thereby deteriorating reading accuracy for the recordedinformation.

[0005] In view of this problem, information reproducing, apparatus forreproducing information recorded on an optical disk are normallyprovided with a tilt servo control device for detecting the tilt betweena pickup as information reading means of the apparatus and the opticaldisk and compensate the tilt by adjusting the direction of the pickup inaccordance with the detected tilt or by providing a signal read out bythe pickup with a tilt correcting process corresponding to the detectedtilt, so as to suppress the deterioration in the information readingaccuracy.

[0006] Further, in order to compensate the tilt, a tilt servo controldevice provided with a liquid crystal panel inserted into the opticalaxis is known (For example, Japanese Patent Laid-Open Publication No.Hei. 11-3531). In the case of the device, the liquid crystal panel isdivided into a plurality of regions, and a phase difference is providedto a light beam passing through each of the regions of the liquidcrystal panel so as to maximize the level of a signal (RF signal) readout from a recording medium by a pickup.

[0007] In optical disks, not only read only optical disks such as aCD-ROM and a DVD-ROM but also writable type optical disks such as aDVD-R, a DVD-RW and a DVD-RAM are included. It is desired that a singleoptical recording/playing apparatus can correspond to optical disks ofany types for the purpose of recording and/or reproducing information.Therefore, it is necessary to mount a tilt servo control device that canproperly perform tilt servo control for optical recording media ofvarious different types in the optical recording/playing apparatus.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention is to providea tilt servo control device and a tilt servo control method that canproperly perform tilt servo control for optical recording media ofvarious different types.

[0009] The present invention provides a tilt servo control device of aninformation recording/reproducing apparatus for recording information onand reproducing information from an optical recording medium set intothe apparatus, the apparatus comprising an optical system for leading alaser beam emitted from a light source to a recording surface of theoptical recording medium and a laser beam reflected by the recordingsurface of the recording medium to a photo detector and a read signalgenerator for generating a read signal in accordance with an outputsignal of the photo detector. The device comprises a recording mediumtype determining device for determining a type of the optical recordingmedium, a tilt drive signal generator for generating a tilt drive signalso as to reduce a tilt angle between a normal to the recording surfaceof the optical recording medium at a position of the laser beamirradiating the recording surface and an optical axis of the laser beamby a method for generating a tilt drive signal corresponding to the typedetermined by the recording medium type determining device, a tilt angleadjuster for adjusting the tilt angle, and a driver for driving the tiltangle adjuster in accordance with the tilt drive signal.

[0010] The present invention provides a tilt servo control method of aninformation recording/reproducing apparatus for recording information onand reproducing information from an optical recording medium set intothe apparatus, the apparatus comprising an optical system for leading alaser beam emitted from a light source to a recording surface of theoptical recording medium and a laser beam reflected by the recordingsurface of the recording medium to a photo detector and a read signalgenerator for generating a read signal in accordance with an outputsignal of the photo detector. The method comprises the steps ofdetermining a type of the optical recording medium, generating a tiltdrive signal so as to reduce a tilt angle between a normal to therecording surface of the optical recording medium at a position of thelaser beam irradiating the recording surface and an optical axis of thelaser beam by a method for generating a tilt drive signal correspondingto the recording medium type, and driving a tilt angle adjuster foradjusting the tilt angle in accordance with the tilt drive signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagram of a disk player provided with a tiltservo control device according to the present invention.

[0012]FIG. 2 is a schematic diagram illustrating the recording format ofa DVD-RW.

[0013]FIG. 3 is a schematic diagram illustrating the recording format ofa general purpose DVD-R.

[0014]FIG. 4 is a diagram illustrating a physical structure of arecording surface of a DVD-RW or DVD-R.

[0015]FIG. 5 is a graph illustrating the waveform of a groove wobblesignal including LLP components.

[0016]FIG. 6 is a schematic diagram illustrating recording tracks of aDVD-RAM.

[0017]FIG. 7 is an enlarged view of a recording surface of the DVD-RAMof FIG. 6.

[0018]FIG. 8 is a schematic diagram illustrating the recording format ofthe header section of each sector located at a changeover point of theDVD-RAM of FIG. 6.

[0019]FIG. 9 is a schematic diagram illustrating the recording format ofthe header section of each sector without a changeover point of theDVD-RAM of FIG. 6.

[0020]FIG. 10 is a schematic diagram illustrating VFO data of a headersection and a data section.

[0021]FIG. 11 is a schematic diagram illustrating different regions of aliquid crystal panel arranged in a pickup of FIG. 1.

[0022]FIG. 12 is a structural diagram schematically illustrating theoptical system of the pickup of FIG. 1.

[0023]FIG. 13 is a schematic diagram illustrating beam spots formed onan optical disk.

[0024]FIG. 14 is a schematic block diagram illustrating a circuitincluding a pickup, a tracking servo circuit and a tilt servo circuit.

[0025]FIG. 15 is a schematic block diagram of a focusing servo circuitand a spindle servo circuit.

[0026]FIG. 16 is a schematic block diagram of a tilt servo drive system.

[0027]FIG. 17 is a flow chart illustrating the operation of a disk typediscriminating circuit.

[0028]FIG. 18 is the remaining portion of the flow chart of FIG. 17.

[0029]FIG. 19 is a graph illustrating the S-characteristics of a CD typedisk and a DVD type disk.

[0030]FIG. 20 is a flow chart of the tilt servo control operation of afirst tilt servo section for a general purpose DVD-R or a DVD-RW.

[0031]FIG. 21 is a flow chart of a tilt servo control operation of thefirst tilt servo section for an authoring purpose DVD-R.

[0032]FIG. 22 is a flow chart of an alternative tilt servo controloperation of the first tilt servo section for an authoring purposeDVD-R.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Embodiments of the present invention will now be described indetail hereinafter with reference to the accompanying drawings.

[0034]FIG. 1 is a schematic block diagram of an optical disk playerprovided with a tilt servo control device according to the presentinvention. In the illustrated optical disk player, a pickup 10irradiates a laser beam onto an optical disk 12 and receives a laserbeam reflected by the optical disk 12. Then, the pickup 10 generates asignal corresponding to the intensity of the received laser beam. Theoptical disk 12 is driven to rotate by a motor 14. The optical disk 12may be a DVD type disk such as a DVD-ROM, a DVD-R, a DVD-RAM and aDVD-RW or a CD type disk such as a CD-ROM and a CD-R. The DVD-RAM hastwo types, a one-recording-layer disk and a two-recording-layer disk.

[0035] Referring to FIG. 2, a DVD-RW has data structure including a PCA(power calibration area), an RMA (recording management area), a lead-inarea, a data area and a lead-out area arranged in the mentioned orderfrom the inner periphery to the outer periphery of the disk. The PCA isan area to be used for a test writing operation so as to determine arecording power level of the laser beam and the RMA is an area wheremanagement information on the current recording operation is written.The lead-in area contains an embossed section comprising phase pitsformed on the disk in advance. The embossed section stores informationon prohibition of copying.

[0036] A DVD-R may be a general purpose disk or an authoring purposedisk. Referring to FIG. 3, a general purpose DVD-R has a data structureincluding a PCA, an RMA, a lead-in area, a data area and a lead-out areaarranged in the mentioned order from the inner periphery to the outerperiphery of the disk. The lead-in area contains in part thereof apre-write section that is located at a position exactly corresponding tothat of the embossed section and used to store information just like theembossed section. On the other hand, an authoring purpose DVD-R does nothave any section that corresponds to the embossed section in FIG. 2 orthe pre-write section in FIG. 3.

[0037]FIG. 4 is a schematic perspective partial view of the recordingsurface of DVD-RW or DVD-R, illustrating its physical structure.Referring to FIG. 4, the recording surface is realized by combining agroove wobble system of wobbled grooves 103, formed between lands 102 ona disk substrate 103, operating as recording tracks and land pre-pits(LPPs) 104 formed in the lands 102 to link adjacent grooves 103.Information is recorded only in grooves 103. The recording surface iscovered by a protection layer 105 typically made of polycarbonate. Thesignals obtained by the groove wobble system are mainly used to controlthe rotation motion of the disk during a recording operation andgenerate recording master clock for recording operations, whereas theLPPs are used for determining the recording position accurately on a bitby bit basis and also for obtaining various pieces of information on thedisk such as pre-addresses. For example, as will be describedhereinafter, the low frequency zone component of the output signal(push-pull signal) of multiplier 44 is the signal that is obtained bythe groove wobble system (groove wobble signal), showing a sinusoidalwaveform as illustrated in FIG. 5. The narrow width pulses produced inparts of the sinusoidal waveform correspond to LPP components that canbe detected by comparing the level of the signal with a threshold valueTH.

[0038] In the case of a DVD-RAM, helical tracks are formed on the diskin a manner as schematically shown in FIG. 6. FIG. 7 is an enlargedschematic perspective partial view of the recording surface of theDVD-RAM of FIG. 6. The tracks are wobbled as shown in FIG. 7. Lands 131and grooves 132 are arranged alternately for the tracks. Changeoverpoints 133 from the lands 131 to the respective grooves 132 are locatedon a same radial line. Data are recorded on the tracks on a sector bysector basis. In other words, a sector provides a unit for recordingdata. Each sector comprises a header section and a data section. Theheader section comprises physically embossed pits 134 that are displacedfrom the center line of the track and located near the boundary with theadjacent track. The data section stores data in the form of phase changepits that are formed by producing changes in the reflectance in therespective areas of the surface of the disk hit by a laser beam. Morespecifically, the changes are produced as a result of phase changes. Thelevel of the signal read from the disk will be affected by the recordingprinciple and the recording conditions of the signal.

[0039]FIG. 8 is a schematic illustration of the recording format of theheader section of a sector located at a changeover point 133. FIG. 9 isa schematic illustration of the header section of a sector not relatedto any changeover point. Referring to FIGS. 8 and 9, the both sectorscomprise a header section having four header fields, a mirror surfacesection located immediately after the header section and a data sectionhaving a land or groove structure as described above. An embossed pit isformed in each of the header fields although not shown in FIGS. 8 and 9.The leading two header fields, or the first and second header fields, ofthe four header fields of each land sector are displaced radiallyinwardly from the center line of the track (by a half of the trackpitch), whereas the remaining two header fields, or the third and fourthheader fields, of the land sector are displaced radially outwardly fromthe center line of the track (by a half of the track pitch). The fourheader fields of each groove sector are mirror images of the headerfields of the corresponding land sector.

[0040] A fixed data section referred to as VFO (variable frequencyoscillator) is arranged in each of the header section and the datasection of each sector as shown in FIG. 10. The VFO data of each VFOshows a predetermined data pattern of repeated “0s” and “1s” for every4T (T representing the bit interval of successive information data). AVFO is arranged at the leading end of each of the first through fourthheader fields of the header section in each sector. First VFO data ofthe first field and the third field have a length equal to 576 clocks,whereas second VFO data of the second field and the fourth field have alength equal to 128 clocks. A VFO data having a length equal to 560clocks is arranged in the data section. For instance, a DVD-RAM containsthese VFO data as part of fixed data without fail.

[0041] A liquid crystal panel 13 is arranged on the optical axis of thebeam of light in the pickup 10 for the purpose of correcting aberrationsin radial directions of the disk in order to make it possible to correctthe wave front aberrations of the optical system. The liquid crystalpanel 13 is typically divided into three regions 13 a through 13 c alonga radial direction as shown in FIG. 11. These regions include an innerperipheral side region, an intermediary region and an outer peripheralside region. The three regions 13 a through 13 c are individually andvariably controlled by the respective drive voltages output from a tiltservo circuit 51 by way of a drive circuit 28 as will be describedhereinafter. With this arrangement, the phase difference of lightpassing through each of the regions 13 a through 13 c can be changedindividually so that the wave front aberrations such as coma that areproduced by a tilt of the disk in a radial direction thereof may becorrected.

[0042] As shown in FIG. 12, the optical system of the pickup 10comprises a semiconductor laser element 21 for emitting a laser beamwith a wavelength of 650 nm for DVDs and a semiconductor laser element22 for emitting a laser beam with a wavelength of 780 nm for CDs. Thesemiconductor laser elements 21, 22 are arranged in such a way that thecenter lines of the laser beams emitted from them are perpendicularrelative to each other. A conflux prism 23 is arranged across the laserbeams emitted from the semiconductor laser elements 21, 22 so that thelaser beam emitted from the semiconductor laser element 21 istransmitted through the conflux prism 23 whereas the laser beam emittedfrom the semiconductor laser element 22 is reflected by the confluxprism 23 and made to leave the latter in a direction same as that of thelaser beam emitted from the semiconductor laser 21.

[0043] The semiconductor laser element 21 is driven by a drive circuit18 whereas the semiconductor laser element 22 is driven by another drivecircuit 19.

[0044] The laser beams coming from the conflux prism 23 are made to getto a polarization beam splitter 26 provided with a polarizer panel 26 aby way of a collimator lens 24 and a grating 25. The grating 25 isarranged to divide the laser beams into a plurality of fluxes (flux of 0order, those of ±1 order). In other words, a main beam and a pair of subbeams are formed by it. The polarization beam splitter 26 allows most(e. g., 90%) of the laser beam entering it to pass through it and thepolarizer panel 26 a transforms the linear polarization of the passinglaser beam into circular polarization.

[0045] The laser beam that is allowed to pass through the polarizationbeam splitter 26 having the polarizer panel 26 a then gets to the disk12 by way of the liquid crystal panel 13 and the objective lens 27thereof and becomes reflected by the recording surface of the disk 12.The laser beam reflected by the recording surface of the disk 12 thenreturns to the polarization beam splitter 26 by way of the liquidcrystal panel 13 and the polarizer panel 26 a. The polarizer panel 26 atransforms the circular polarization of the reflected and returned laserbeam into linear polarization. The polarization beam splitter 26reflects the returned laser beam by means of its polarizing/splittingplane 26 b. The reflected laser beam then gets to the light receivingplane of photo detector 30 by way of condenser lens 28 and multi lens29.

[0046] The pickup 10 further comprises an actuator 34 having a focusingsection for moving the objective lens 27 along the optical axis and atracking section for moving the objective lens 27 in a radial directionof the disk that is perpendicular to the optical axis.

[0047] As shown in FIG. 13, spots MS, SS1, SS2 are formed on the disk 12by the main beam and the sub beams of the laser beam coming from thepickup 10. Note that the two sub beam spots SS1, SS2 are displaced fromthe main beam spot MS in a radial direction of the disk by a half of thetrack pitch P. This is because the differential push-pull method is usedfor detecting tracking errors.

[0048] As shown in FIGS. 13 and 14, the photo detector 30 comprises alight receiving section 31 for receiving a main beam and a pair of lightreceiving sections 32, 33 for receiving sub beams arranged at oppositesides of the light receiving section 31. The light receiving surface ofthe light receiving section 31 is divided into four areas to producephoto detecting elements 31 a through 31 d, whereas the light receivingsurfaces of the light receiving sections 32, 33 are divided into twoareas to produce photo detecting elements 32 a, 32 b and 33 a, 33 b.

[0049] As shown in FIG. 14, the pickup 10 comprises an adder 35 foradding the output signal a of the photo detecting element 31 a and theoutput signal c of the photo detecting element 31 c, another adder 36for adding the output signal b of the photo detecting element 31 b andthe output signal d of the photo detecting element 31 d and stillanother adder 37 for outputting an RF signal (read signal) by adding theoutput signals of the adders 35, 36. The output of the adder 37 isconnected to the tilt servo circuit 51 and the disk type discriminatingcircuit 52 of a servo circuit 5 as well as to a reproduction processingsection (not shown). The outputs of the adders 35, 36 are connected to afocusing servo circuit 53.

[0050] As shown in FIG. 15, the focusing servo circuit 53 comprises anamplifier 61 for amplifying the output signal of the adder 35, anotheramplifier 62 for amplifying the output signal of the adder 36, asubtracter 63 for generating a focus error signal FE by subtracting theoutput signal of the amplifier 62 from the output signal of theamplifier 61, an equalizer 64 for generating a focus drive signal FD inaccordance with the focus error signal FE that is the output signal ofthe subtracter 63, a switch 65, still another adder 66 and a voltageapplication circuit 67 for generating a variable voltage. The focusdrive signal FD output from the equalizer 64 is fed to drive circuit 68by way of the switch 65 and the adder 66 when the switch 65 is on. Thedrive circuit 68 drives the focusing section of the actuator 34 inaccordance with the focus drive signal FD. The on/off operations of theswitch 65 are controlled by the system control circuit 1. The voltageapplication circuit 67 generates a variable voltage in accordance withthe focus jump command from the system control circuit 6. As a variablevoltage is generated by the voltage application circuit 67, it is addedby the adder 66 and the output signal of the adder 66 become the focusdrive signal FD.

[0051] The pickup 10 additionally comprises an adder 38 for adding theoutput signal a of the photo detecting element 31 a and the outputsignal d of the photo detecting element 31 d, another adder 39 foradding the output signal b of the photo detecting element 31 b and theoutput signal c of the photo detecting element 31 c and a subtracter 40for subtracting the output signal of the adder 39 from that of the adder38. The output of the subtracter 40 is connected to the disk typediscriminating circuit 52 and the tracking servo circuit 54 of the servocircuit 5. The output signal of the subtracter 40 is a push-pull signal.

[0052] As shown in FIG. 14, the pickup 10 further comprises a subtracter41 for subtracting the output signal of the photo detecting element 32 bfrom the output signal of the photo detecting element 32 a and anothersubtracter 42 for subtracting the output signal of the photo detectingelement 33 b from the output signal of the photo detecting element 33 a.The outputs of the subtracters 41, 42 are connected to the trackingservo circuit 54.

[0053] As shown in FIG. 14, the tracking servo circuit 54 comprises anadder for adding the output signals of the subtracters 41, 42, amultiplier 44 for multiplying the output signal of the adder 43 by acoefficient α, a subtracter 45 for generating a differential push-pulltracking error signal TE by subtracting the output signal of themultiplier 44 from the output signal (push-pull signal) of thesubtracter 40, an equalizer 46 for generating a tracking drive signal TDin accordance with the tracking error signal TE output from thesubtracter 45 and a switch 47.

[0054] The coefficient a of the adder 44 is determined in such a waythat the output signal (push-pull of the main beam) of the subtracter 40and the output signal (push-pull of the sub beams) of the multiplier 44are made substantially equal to each other. Note that these two outputsignals have respective AC components whose polarities are opposite toeach other and respective DC components that show a same polarity.

[0055] The equalizer 46 generates the tracking drive signal TD so as toreduce the tracking error signal TE. The tracking drive signal TD outputfrom the equalizer 46 is fed to the drive circuit 48 by way of theswitch 47 when the switch 47 is on. The drive circuit 48 drives thetracking section of the actuator 34 in accordance with the trackingdrive signal TD. The on/off operations of the switch 47 are controlledby the system control circuit 1.

[0056] The tilt servo circuit 51 generates a tilt drive signal TID fordriving the above described liquid crystal panel 13 and is provided withthree tilt servo sections, or the first through third tilt servosections, that are adapted to selectively operate depending on the typeof the disk 12. The first tilt servo section is used for DVD-Rs andDVD-RWs and, as shown in FIG. 14, comprises an adder 69, a low passfilter 73, a changeover switch 70, a reference memory 71, a subtracter72, an A/D converter 74 and a tilt correction ROM 75. The adder 69 addsthe output signal of the subtracter 40 in the pickup 10 and that of themultiplier 44 in the tracking servo circuit 54.

[0057] Since the coefficient a of the multiplier 44 is determined in amanner as described above, the push-pull component of the output of theadder 69 is cancelled to leave only the DC component. The output signalof the adder 69 is smoothed as it is input to the low pass filter 73 sothat the eccentric component of the disk will be removed. The outputsignal of the low pass filter 73 is supplied to the reference memory 71by way of the changeover switch 70 to represents a state involving notilt before an information recording operation and the reference memory71 stores the supplied signal level as reference signal. The changeoverswitch 70 relays the output signal of the low pass filter 73 to thesubtracter 72 during a recording operation. During a recordingoperation, the output signal of the low pass filter 73 is a push-pullsignal containing an offset component that varies as a function of thetilt of the disk 12, or a push-pull offset signal. The subtracter 72generates a first tilt error signal representing the tilt of the disk 12by subtracting the reference signal stored in the reference memory 71from the output signal of the adder 69.

[0058] During a recording operation, the output signal of the multiplier44 and that of the subtracter 40 are tracking error signals containingan offset component that represents the tilt of the disk 12. The signalobtained by removing the offset component from the signal produced asthe sum of the two signals by means of the adder 69 is stored in thereference memory 71 as reference signal. Thus, the signal output fromthe subtracter 72 as a result of subtracting the reference signal fromthe output signal of the adder 69 contains only the offset component sothat it is possible to provide the first tilt error signal.

[0059] The first tilt error signal is digitized by the A/D converter 74and then fed to the tilt correction ROM 75, which stores a plurality oftilt correction values and output three correction values stored at therespective addresses specified by the first tilt error signal. Thesethree correction values correspond respectively to the three regions 13a through 13 c of the liquid crystal panel 13.

[0060] While the low pass filter 73 is provided in this embodiment, itmay be omitted and the first tilt error signal may be obtained directlyfrom the subtracter 72 when the eccentric component of the disk issmall.

[0061] Additionally, while the output signal of the subtracter 40 andthat of the multiplier 44 are added by the adder 70 in this embodiment,it may alternatively be so arranged that only either the output signal(main push-pull signal) of the subtracter 40 or the output signal (subpush-pull signal) of the multiplier 44 is smoothed by the low passfilter and fed to the reference memory 71 by way of the changeoverswitch 70.

[0062] As shown in FIG. 14, the second tilt servo section that is usedfor DVD-RAMs comprises a delay circuit 76, a subtracter 77, a low passfilter 78, an A/D converter 79 and a tilt correction ROM 80. The delaycircuit 76 delays the RF signal output form the adder 37 and supplies itto the subtracter 77. The RF signal corresponds to the first VFO data(of 64 bytes) in the first and third header fields of the abovedescribed header format of DVD-RAM. The delay time of the delay circuit76 corresponds to the time necessary for passing through the firstheader field and the second header filed of the header section. Thus,while the first VFO data of the first header field is fed from the delaycircuit 76 to one of the input terminals (non-inversion input terminal)of the subtracter 77, the first VFO data of the third header field isfed to the other input terminal (inversion input terminal) of thesubtracter 77. The subtracter 77 subtracts the first VFO data of thethird head field from the first VFO data of the first header field andsupplies a signal representing the different to the low pass filter 78.The low pass filter 78 smooths the signal obtained by the subtractionand generates a second tilt error signal. The second tilt error signalis digitized by the A/D converter 79 and then fed to the tilt correctionROM 80, which stores a plurality of tilt correction values and outputthree correction values stored at the respective addresses specified bythe second tilt error signal. These three correction values output fromthe tilt correction ROM 80 correspond respectively to the three regions13 a through 13 c of the liquid crystal panel 13. Japanese PatentLaid-Open Publication No. 2000-137923 describes the generation of tilterror signal of a tilt servo section to be used for DVD-RAMs in greaterdetail.

[0063] The third tilt servo section for DVD-ROMs uses a socalled hillclimbing method for the purpose of generating correction values in orderto maximize the RF signal. As shown in FIG. 14, it comprises an RFamplitude level detector 81, an L register 82, an H register 83, acomparator 84, an up-down counter 85, an adder and a tilt correction ROM87. The RF amplitude level detector 81 detects the amplitude level ofthe RF signal. The L register 82 holds the amplitude level of the RFsignal obtained by using the current output value of the up-down counter85 as address value for the tilt correction ROM 87. The H register 83holds the amplitude level of the RF signal obtained by adding the outputvalue of the up-down counter 85 and 1 by means of the adder 86 and usingthe sum as address value for the tilt correction ROM 87. The adder 86performs the addition of 1 in response to the command from the systemcontrol circuit 1. The comparator 84 compares the amplitude level heldin the L register 82 and the one held in the H register 83. If the valueheld in the L register 82 is found to be larger than the value held inthe H register 83 as a result of the comparison made by the comparator84, the up-down counter 85 counts up by 1. If, on the other hand, thevalue held in the L register 82 is found to be smaller than the valueheld in the H register 83 as a result of the comparison made by thecomparator 84, the up-down counter 85 counts down by 1. The tiltcorrection ROM 87 outputs the correction values stored at the respectiveaddresses specified by the output value of the adder 86. The threecorrection values output from the tilt correction ROM 87 correspondrespectively to the three regions 13 a through 13 c of the liquidcrystal panel 13.

[0064] As a tilt servo start command is issued to the above describedtilt servo section for DVD-ROMs, the current output value of the up-downcounter 85 is set in the tilt correction ROM 87 by way of the adder 86as address value. Then, as a result, the liquid crystal panel 13 isdriven by way of a servo drive system, which will be describedhereinafter. The amplitude level of the RF signal detected by the RFamplitude level detector 81 is held by the L register 82. Then, 1 isadded to the current output value of the up-down counter 85 by the adder86 and the sum is set in the tilt correction ROM 87 as address value andused to drive the liquid crystal panel 13 by way of the tilt servo drivesystem. The amplitude level of the RF signal detected by the RFamplitude level detector 81 is held by the H register 83. The comparator84 compares the value held by the L register 82 with the value held bythe H register 83 and counts up 1 by when the value held by the Lregister 82 is larger than the value held by the H register 83, whereasit counts down by 1 when the value held by the L register 82 is smallerthan the value held by the H register 83. Then, the above operation isrepeated. Japanese Patent Laid-Open Publication No. Hei. 11-3531describes such a tilt servo section for DVD-ROMs in greater detail.

[0065] The outputs of the three tilt correction ROMs 75, 80, 87 areconnected to selector 88 and then to tilt servo drive system comprisingregisters 96 a through 96 c, PWM sections 97 a through 97 c and a drivecircuit 28. The selector 88, the registers 96 a through 96 c, and thePWM sections 97 a through 97 c are contained in the servo circuit 5. Theselector 88 relays one of the corrected output values of the tiltcorrection ROMs 75, 80, 87. The output of the selector 88 is connectedto the registers 96 a through 96 c for holding a corrected value. Theoutputs of the registers 96 a through 96 c are connected to therespective PWM (pulse width modulator) sections 97 a through 97 c. ThePWM sections 97 a through 97 c perform pulse-width modulates inaccordance with the respective output values of the registers 96 athrough 96 c and supply the respective modulated signals to the drivecircuit 28 as tilt drive signals TID.

[0066] Regardless which one of the tilt correction ROMs 75, 80, 87supplies a corrected value to the registers 96 a through 96 c of thetilt servo drive system by way of the selector 88, the corrected valueheld by the register 96 a and the one held by the register 96 c aresymmetrical relative to the corrected value held by the register 96 b. Adrive signal having a pulse width corresponding to the corrected valueheld by the register 96 a is generated by the PWM section 97 a.Similarly, a drive signal having a pulse width corresponding to thecorrected value held by the register 96 b is generated by the PWMsection 97 b. Likewise, a drive signal having a pulse widthcorresponding to the corrected value held by the register 96 c isgenerated by the PWM section 97 c. The drive circuit 28 applies voltagesrespectively to the regions 13 a through 13 c in accordance with therespective levels of the corresponding drive signals. As a result of thevoltage application, a light path difference Δn·d (Δn is the variationof the refractive index and d is the liquid crystal cell thickness) isproduced by the double refraction effect of liquid crystal molecules inthe regions 13 a through 13 c. If the wavelength of a light beam passingthrough the liquid crystal is λ, a phase difference of Δn·d (2π/λ) isgiven to the light beam. Thus, it is now possible to correct theaberrations including the coma generated in a radial direction of thedisk due to the tile of the disk.

[0067] As shown in FIG. 15, the servo circuit 5 has a spindle servocircuit 93 comprising a rotational speed detector 89, a rotational speederror generator 90, an equalizer 91 and a switch 92. A frequency signalFG is fed to the rotational speed detector 89. A frequency signal FG isan AC signal representing the current revolution frequency of thespindle motor 14 for driving the optical disk 12 to rotate by way of aturn table. The rotational speed detector 89 generates a rotationalspeed signal indicating the rotational speed of the spindle motor thatcorresponds to the frequency signal FG and supplies it to the systemcontrol circuit 1 and also to the rotational speed error generatingsection 90. The rotational speed error generating section 90 generates arotational speed error signal indicating the difference between therotational speed signal and the reference rotational speed signal fedfrom the system control circuit 1 and supplies it to the equalizer 91.In response to the rotational speed error signal, the equalizer 91generates a spindle drive signal SPD, which is fed to the spindle motor14 by way of the drive circuit 83 when the switch 92 is on. The spindlemotor 14 drives the optical disk 12 to rotate with the rotational speedindicated by the spindle drive signal SPD. The AC generator (not shown)arranged in the spindle motor 14 supplies the frequency signal FGrepresenting the current revolution frequency to the servo circuit 5.Thus, with the above-described arrangement of the spindle servo system,the spindle motor 14 is driven to rotate with the rotational speedindicated by the reference rotational speed signal fed from the systemcontrol circuit 1.

[0068] Although not shown, the servo circuit 5 generates a slider drivesignal SD on the basis of the above tracking error signal TE andsupplies it to the slider 100 by way of the drive circuit 8. As aresult, the slider 100 moves the pickup 10 in a radial direction of thedisk with a rotational speed corresponding to the drive current based onthe slider drive signal SD.

[0069] The disk type discriminating circuit 52 determines the type ofthe disk 12 mounted on the turn table. As pointed out earlier, the disks12 may be a CD type disk such as CD, CD-ROM or CD-R or a DVD type disksuch as DVD, DVD-ROM, DVD-R, DVD-RAM or DVD-RW.

[0070] Now, the operation of the disk discriminating circuit 52 will bedescribed by referring to the flow charts of FIGS. 17 and 18.

[0071] Firstly, referring to FIG. 17, the disk discriminating circuit 52determines if a recording command is issued from the system controlcircuit 1 or not (Step S1). If it is determined that a recording commandis issued, it determines if the disk 12 is of the CD type or of the DVDtype (Step S2). A CD type disk may be a CD, a CD-ROM or a CD-R. A DVDtype disk may be a DVD, a DVD-ROM, a DVD-R, a DVD-RAM or a DVD-RW. Forthe operation of Step S2, a laser beam having a wavelength of 780 nm isemitted from the semiconductor laser element 22 for CDs at a readingpower level and the disk 12 is driven to rotate as the switch 92 isturned on. Then, a variable voltage is supplied from the voltageapplication circuit 67 to the drive circuit 68 by way of the adder 66 toforcibly drive the focus actuator section and continuously move thefocused position on the disk 12. As the focused position is moved, theS-characteristic of the focus error signal FE is observed. As shown inFIG. 19, the S-characteristic appears when the focused position islocated on the disk surface and when it is located on the pit producingsurface. The time interval from the appearance of S due to the disksurface and the one due to the pit producing surface is observed. Asseen from FIG. 19, the time interval A from the appearance of S due tothe disk surface and the one due to the pit producing surface of a DVDtype disk is shorter than the corresponding time interval B of a CD typedisk. Therefore, if the observed time interval is greater than apredetermined time threshold value, the disk is determined to be a CDtype disk. On the other hand, if the observed time interval is smallerthan the predetermined time threshold value, the disk is determined tobe DVD type disk.

[0072] If it is determined in Step S2 that the disk is of the DVD type,the disk discriminating circuit 52 further determines if the disk 12belongs to the first category covering single-layered DVD-ROMs andDVD-Rs or the second category covering double-layered DVD-ROMs, DVD-RAMsand DVD-RWs (Step S3). In the operation of Step S3, a laser beam havinga wavelength of 650 nm is emitted from the semiconductor laser element21 for DVDs at the reading power level and the disk 12 is driven torotate as the switch 92 is turned on. Then, a variable voltage issupplied from the voltage application circuit 67 to the drive circuit 68by way of the adder 66 to forcibly drive the focus actuator section andcontinuously move the focused position on the disk 12. As the focusedposition is moved, the S-characteristic of the focus error signal FEcorresponding the pit producing surface is observed. The amplitude ofthe S formed by the pit producing surface of a single-layered DVD-ROM ora DVD-R is greater than its counterpart of a double-layered DVD-ROM, aDVD-RAM or a DVD-RW. Generally, DVD-RAMs and DVD-RWs, that arerewritable disks, are made of a phase change material and hence show alow reflectance. Double layered DVD-ROMs are made semitransparent in thepit producing surface and hence show a low reflectance. A disk showing alow reflectance also shows an S having a small amplitude. Thus, the disk12 is determined to be either a single-layered DVD-ROM or a DVD-R of thefirst category when the amplitude of the S is smaller than apredetermined threshold value, whereas it is determined to be adouble-layered DVD-ROM, a DVD-RAM or a DVD-RW of the second category.

[0073] If, in Step S3, it is determined that the disk belongs to thefirst category and hence is either a single-layered DVD-ROM or a DVD-R,it is then determined if the disk 12 is a single-layered DVD-ROM or aDVD-R (Step S4). In the disk discriminating operation of Step S4, alaser beam having a wavelength of 650 nm is emitted from thesemiconductor laser element 21 for DVDs at the reading power level andthe disk 12 is driven to rotate as the switch 92 is turned on as in StepS3. However, the supply of the variable voltage from the voltageapplication circuit 67 is suspended. Then, the switch 65 is turned onand the focusing servo circuit 53 performs a focusing operation.Additionally, the switch 47 is turned on and the tracking servo circuit54 performs a tracking operation. Under this condition, it is determinedif the RF signal or the tracking error signal being read contains agroove wobble signal component or not. If a groove wobble signalcomponent is detected, the disk is determined to be a DVD-R. If, on theother hand, no groove wobble signal component is detected, the disk isdetermined to be a single-layered DVD-ROM.

[0074] As shown in FIG. 4, in case of DVD-R and DVD-RW groove wobbles103 are formed on the pit producing surface and LPPs (land pre-pits) 104are formed between adjacent groove wobbles 103. The LPPs 104 are usedfor accurately determining the recording position on the basis of a unitof bit and obtaining various pieces of information on the disk includingpre-addresses.

[0075] If, on the other hand, it is determined in Step S4 that the disk12 is a DVD-R, it is then determined if the DVD-R is a general purposeDVD-R or an authoring purpose DVD-R (Step S5). More specifically, theinformation of the LPPs is read out to see if the DVD-R is a generalpurpose DVD-R or an authoring DVD-R after the determination of thecategory of the disk in Step S4.

[0076] If, in Step S5, it is determined that the disk 12 is an authoringpurpose DVD-R, the system control circuit 1 controls the recordingoperation for the authoring purpose DVD-R. If, on the other hand, it isdetermined in Step S5 that the disk 12 is a general DVD-R, the systemcontrol circuit 1 controls the recording operation for the generalpurpose DVD-R and DVD-RW. The first tilt servo section for DVD-Rs andDVD-RWs is used for controlling the recording operation for an authoringpurpose DVD-R, a general purpose DVD-R or a DVD-RW. More specifically,the selector 88 relays the output values of the tilt correction ROM 75to the registers 96 a through 96 c in accordance with the command fromthe system control circuit 1, respectively.

[0077] If it is determined in Step S4 that the disk 12 is asingle-layered DVD-ROM, an impossible recording message is displayed ona display (not shown) (Step S6).

[0078] If it is determined in Step S3 that the disk 12 belongs to thesecond category and may be a double-layered DVD-ROM, a DVD-RAM or aDVD-RW, it is then determined if the disk 12 is a double-layered DVD-ROMor not and hence a DVD-RW or a DVD-RAM (Step S7). In Step S7, a laserbeam having a wavelength of 650 nm is emitted from the semiconductorlaser element 21 for DVDs at the reading power level and the disk 12 isdriven to rotate as the switch 92 is turned on as in Step S3. However,the supply of the variable voltage from the voltage application circuit67 is suspended. Then, the switch 65 is turned on and the focusing servocircuit 53 performs a focusing operation. Additionally, the switch 47 isturned on and the tracking servo circuit 54 performs a trackingoperation. Under this condition, it is determined if the RF signal orthe tracking error signal being read contains a groove wobble signalcomponent or not. If a groove wobble signal component is detected, thedisk is determined to be a DVD-RW or a DVD-RAM. If, on the other hand,no groove wobble signal component is detected, the disk is determined tobe a double-layered DVD-ROM.

[0079] If it is determined in Step S7 that the disk 12 is adouble-layered DVD-ROM, the processing operation proceeds to Step S6 andan impossible recording message is displayed on a display screen (notshown).

[0080] If it is determined in Step S7 that the disk 12 is either aDVD-RW or a DVD-RAM, then it is determined if the disk 12 is in fact aDVD-RW or a DVD-RAM (Step S8). The operation of driving the disk playerin Step S6 is continued to Step S8. Thus, it is determined if thepush-pull signal such as a tracking error signal TE contains an LPPsignal component corresponding to an LPP or not. If an LPP signalcomponent is detected in the push-pull signal, the disk 12 is determinedto be a DVD-RW. If, on the other hand, no LPP signal component isdetected, the disk 12 is determined to be a DVD-RAM.

[0081] If, in Step S8, it is determined that the disk 12 is a DVD-RW,the system control circuit 1 controls the recording operation for ageneral purpose DVD-R or a DVD-RW. If, on the other hand, it isdetermined in Step S8 that the disk is a DVD-RAM, the system controlcircuit 1 controls the recording operation for the general purposeDVD-RAM. The second tilt servo section for DVD-RAMs is used forcontrolling the recording operation for a DVD-RAM. More specifically,the selector 88 relays the output values of the tilt correction ROM 80to the registers 96 a through 96 c in response to the command from thesystem control circuit 1, respectively.

[0082] If it is determined in Step S2 that the disk is of the CD type,it is further determined if the disk 12 is a CD-ROM or a CD-R (Step S9).In the determination of Step S9, a laser beam having a wavelength of 780nm is emitted from the semiconductor laser element 22 for CDs at thereading power level and the disk 12 is driven to rotate as the switch 92is turned on as in Step S2. However, the supply of the variable voltagefrom the voltage application circuit 67 is suspended. Then, the switch65 is turned on and the focusing servo circuit 53 performs a focusingoperation. Additionally, the switch 47 is turned on and the trackingservo circuit 54 performs a tracking operation. Under this condition, itis determined if the RF signal or the tracking error signal TE beingread contains a groove wobble signal component or not. If a groovewobble signal component is detected, the disk is determined to be aCD-R. If, on the other hand, no groove wobble signal component isdetected, the disk is determined to be a CD-ROM.

[0083] If it is determined in Step S9 that the disk 12 is a CD-ROM, theprocessing operation proceeds to Step S10 and an impossible recordingmessage is displayed on a display screen (not shown) as in Step S6.

[0084] If, on the other hand, it is determined in Step S9 that the diskis a CD-R, the system control circuit 1 controls the signal recordingoperation for the CD-R. In the recording operation for the CD-R, no tiltservo control is performed.

[0085] If it is determined in Step S1 that no recording command isissued, it is then determined if a playback command is issued from thesystem control circuit 1 or not (Step S11). If it is determined that theplayback command is issued, it is then determined if the disk 12 is ofthe CD type or of the DVD type (Step S12). The processing operation ofStep S12 is similar to that of Step S2.

[0086] If it is determine in Step S12 that the disk 12 is of the CDtype, the system control circuit 1 controls playback operation for theCD type disk. No tilt servo control operation is performed in theplayback operation for the CD type disk.

[0087] If, on the other hand, it is determined in Step S12 that the diskis of the DVD type, it is then determined if the disk 12 is a DVD-RAM ornot (Step S13). In the operation of Step S13, a laser beam having awavelength of 650 nm is emitted from the semiconductor laser element 21for DVDs at the reading power level and the disk 12 is driven to rotateas the switch 92 is turned on. Then, a variable voltage is supplied fromthe voltage application circuit 67 to the drive circuit 68 by way of theadder 66 to forcibly drive the focus actuator section and continuouslymove the focused position on the disk 12. As the focused position ismoved, the S-characteristic of the focus error signal FE thatcorresponds to the bit producing surface is observed. After thesuspension of the supply of the variable voltage from the voltageapplication circuit 67, the switch 65 is turned on and the focusingservo circuit 53 performs a focusing operation. Additionally, the switch47 is turned on and the tracking servo circuit 54 performs a trackingoperation. Under this condition, it is determined if the push-pullsignal such as tracking error signal TE contains an LPP signal componentcorresponding to an LPP or not. If the amplitude of the S is less than athreshold value and the push-pull signal does not contain any LPP signalcomponent, the disk is determined to be a DVD-RAM.

[0088] If it is determined in Step S13 that the disk 12 is a DVD-RAM,the system control circuit 1 controls playback operation for theDVD-RAM. If, on the other hand, it is determined in Step S13 that thedisk 12 is a DVD type disk other than a DVD-RAM, the system controlcircuit 1 controls playback operation for the DVD-ROM. In the playbackoperation for the DVD-ROM, a tilt servo section for DVD-ROMs is used. Inother words, the selector 88 relays the output values of the tiltcorrection ROM 87 to the registers 96 a through 96 c in response to thecommand from the system control circuit 1, respectively.

[0089] For the purpose of the invention, the above described diskdiscriminating method may be replaced by some other disk discriminatingmethod such as one for detecting the contents of the TOC of the opticaldisk.

[0090] Now, the control operation of the first tilt servo section whenthe disk 12 is a DVD-R or a DVD-RW will be discussed below.

[0091] Firstly, for controlling the operation of recording a signal on ageneral purpose DVD-R or a DVD-RW, the system control circuit 1 forciblydrives the slider 100 by means of the drive circuit 8 to move the pickup10 onto the embossed section (pre-write) section of the disk 12 andforcibly rotate the disk (Step S21). The forced rotation is typicallyrealized by feeding a spindle drive signal SPD for predeterminedrotational speed to the drive circuit 83 from an appropriate circuit(not shown). Additionally, the system control circuit 1 causes the drivecircuit 18 to drive the semiconductor laser element 21 for DVDs and makethe latter emit a laser beam having a wavelength of 650 nm at thereading power level (Step S22) and turns on the switch 92 to drive thedisk 12 to rotate under the control of the spindle servo circuit 93 forspindle rotation. Furthermore, the system control circuit 1 turns on theswitch 65 to make the focusing servo circuit 53 operate for focusing andalso the switch 47 to make the tracking servo circuit 54 operate fortracking (Step S23). Alternatively, it may be so arranged that avariable bias voltage is multiplexed with the tracking error signal todetect the bias voltage that maximizes the RF signal level.

[0092] Then, the focusing servo circuit 53 detects an optimal level ofthe RF signal by means of offset regulation (Step S24). In other words,the focusing servo circuit 53 multiplexes the focus error signal withthe bias voltage from a bias circuit (not shown) and the bias voltage ismade to vary to find out the bias voltage level that maximizes the RFsignal level. Thereafter, the regions 13 a through 13 c of the liquidcrystal panel 13 are driven by the tilt servo system to detect theoptimum RF signal level (Step S25). More specifically, the correctionvalues of the regions 13 a through 13 c that correspond to therespective addresses of the tilt correction ROM 75 are read out andsequentially fed to the respective registers 96 a through 96 c by way ofthe selector 88. Then, the PWM sections 97 a through 97 c are drive togenerate tilt drive signals TID in order to drive the respective regions13 a through 13 c of the liquid crystal panel 13 by way of the drivecircuit 28 so that the address value or the three correction values thatmaximize the RF signal level may be detected.

[0093] When the optimum RF signal level is detected, the level of theoutput signal of the adder 69 is stored in the reference memory 71 asreference signal (Step S26). The changeover switch 72 relays the outputsignal of the adder 69 to the reference memory 71 while the processingoperation of Step S26 is being carrier out but, when the operation ofStep S26 is over, it is switched to relay the output signal of the adder69, which is a push-pull offset signal, to the subtracter 72. Then, itperforms a tentative writing operation in the PCA area of the disk todetermine an optimal recording power level of the laser beam (Step S27).Thereafter, it starts a recording operation (Step S28) and drives theregions 13 a through 13 c of the liquid crystal panel 13 according tothe tilt signal computationally determined by the first tilt servosection for DVD-Rs and DVD-RWs (Step S29). More specifically, leveldifference signal representing the level difference between the outputsignal of the adder 69 and the reference signal stored in the referencememory 71 is produced from the subtracter 72 and supplied to the A/Dconverter 74 by way of the low pass filter 73 as tilt error signal. Theoutput signal of the A/D converter 74 represents addresses in the tiltcorrection ROM 75 and three correction values corresponding to theaddresses are read out of the tilt correction ROM 75. The threecorrection values are then fed to the respective registers 96 a through96 c by way of the selector 88 so that the PWM sections 97 a through 97c generate corresponding tilt drive signals TID, which are then used bythe drive circuit 28 to drive the respective regions 13 a through 13 cof the liquid crystal panel 13. The processing operation of Step S29continues until the recording operation ends.

[0094] For controlling the recording operation on the authoring purposeDVD-R, the system control circuit 1 forcibly drives the slider 100 bymeans of the drive circuit 8 so as to move the pickup 10 to the PCA areaof the disk 12 and forcibly rotate the disk 12 (Step S31). Then, itissues a command for driving the semiconductor laser element 21 for DVDsto emit a laser beam having a wavelength of 650 nm at the recordingpower level (Step S32). The system control circuit 1 then turns on theswitch 92 to drive the disk 12 to rotate under the control of thespindle servo circuit 93 for spindle rotation. Furthermore, the systemcontrol circuit 1 turns on the switch 65 to make the focusing servocircuit 53 operate for focusing and also the switch 47 to make thetracking servo circuit 54 operate for tracking (Step S33). Then, itperforms a tentative writing operation in the PCA area of the disk todetermine an optimal recording power level of the laser beam (Step S34).Subsequently, it changes the recording power level stepwise topreliminarily determine an optimum recording power level.

[0095] After carrying out Step S27, the system control circuit 1 issuesa command for driving the semiconductor laser element 21 for DVDs toemit a laser beam having a wavelength of 650 nm at the reading powerlevel to the tentatively written pit (Step S35) and causes the focusingservo circuit 53 to detect an optimum RF signal level by means of offsetregulation (Step S36). More specifically, the focusing servo circuit 53multiplexes the focus error signal with the bias voltage from a biascircuit (not shown) and the bias voltage is made to vary to find out thebias voltage level that maximizes the RF signal level. It may be soarranged that the tracking servo circuit 54 also detects an optimum RFsignal level also by means of offset regulation at the same time.Thereafter, the regions 13 a through 13 c of the liquid crystal panel 13are driven by the tilt servo system to detect the optimum RF signallevel (Step S37). More specifically, the correction values of theregions 13 a through 13 c that correspond to the respective addresses ofthe tilt correction ROM 75 are read out and sequentially fed to therespective registers 96 a through 96 c by way of the selector 88. Then,the PWM sections 97 a through 97 c are driven to generate tilt drivesignals TID in order to drive the respective regions 13 a through 13 cof the liquid crystal panel 13 by way of the drive circuit 28 so thatthe address value or the three correction values that maximize the RFsignal level may be detected.

[0096] When the optimum RF signal level is detected, the level of theoutput signal of the adder 69 is stored in the reference memory 71 asreference signal (Step S38). The changeover switch 70 relays the outputsignal of the adder 69 to the reference memory 71 while the processingoperation of Step S38 is being carrier out but, when the operation ofStep S38 is over, it is switched to relay the output signal of the adder69, which is a push-pull offset signal, to the subtracter 72. Then, itperforms a tentative writing operation in the PCA area of the disk todetermine an optimal recording power level of the laser beam (Step S39).Thereafter, it starts a recording operation (Step S40) and drives theregions 13 a through 13 c of the liquid crystal panel 13 according tothe tilt error signal computationally determined by the first tilt servosection for DVD-Rs and DVD-RWs (Step S41). The processing operation ofStep S41 continues until the recording operation ends.

[0097] The user can pre-write management information or the like on anauthoring purpose DVD-R. FIG. 22 is a flow chart of a tilt servo controloperation of the first tilt servo section that can be used for anauthoring purpose DVD-R when the use of the pre-write feature isinvolved. Referring to FIG. 22, after carrying out Steps S31 throughS34, the system control circuit 1 forcibly drives the slider 100 bymeans of the drive circuit 8 to move the pickup 10 onto the pre-writesection for a pre-write operation (which corresponds to the pre-writesection of a general purpose DVD) of the disk 12 (Step S61) and issues acommand for driving the semiconductor laser element 21 for DVDs to emita laser beam having a wavelength of 650 nm at a preliminarily determinedoptimum recording power level (Step S62) and write a signal in thepre-write section of the disk with the preliminarily determined optimumrecording power level (Step S63). After Step S63, the system controlcircuit 1 issues a command for driving the semiconductor laser element21 for DVDs to emit a laser beam having a 650 nm at the reading powerlevel (Step S64) and then proceeds to Step S36, where it causes thefocusing servo circuit 53 to detects an optimum RF signal level by meansof offset regulation. Thereafter, the system control circuit 1 performsSteps S37 through S41. Note that the system control circuit 1 forciblydrives the slider 100 by means of the drive circuit 8 to move the pickup10 onto the PCA area of the disk 12 before executing Step S39 (StepS65).

[0098] While a tilt servo control device including a liquid crystalpanel 13 is used as tilt angle adjusting means for compensating the tiltangle in the above embodiment, an actuator for mechanically regulatingthe inclination of the pickup or the objective lens relative to theoptical disk may be used to replace the tilt servo control device. Then,the actuator will be driven in accordance with a tilt error signal.

[0099] As described above in detail, according to the invention, thereare provided a tilt servo control device and a tilt servo control methodthat can be used with mint optical recording media bearing no writteninformation for the purpose of tilt servo control operations.

[0100] The present invention can be applied to not only an optical diskplayer with a recording function but also an optical disk player withouta recording function.

[0101] According to the invention, since the type of an opticalrecording medium set in the recording/reproducing apparatus isdetermined and a method for generating a tilt drive signal correspondingto the determination is selected, the tilt servo can be properlycontrolled for optical recording media of various different types.

[0102] This application is based on Japanese Patent Application No.2000-367305 which is hereby incorporated by reference.

What is claimed is:
 1. A tilt servo control device of an informationrecording/reproducing apparatus for recording information on andreproducing information from an optical recording medium set into saidapparatus, said apparatus comprising an optical system for leading alaser beam emitted from a light source to a recording surface of theoptical recording medium and a laser beam reflected by the recordingsurface of the recording medium to a photo detector and a read signalgenerator for generating a read signal in accordance with an outputsignal of the photo detector, said device comprising: a recording mediumtype determining device for determining a type of said optical recordingmedium; a tilt drive signal generator for generating a tilt drive signalso as to reduce a tilt angle between a normal to the recording surfaceof said optical recording medium at a position of said laser beamirradiating said recording surface and an optical axis of said laserbeam by a method for generating a tilt drive signal corresponding to thetype determined by said recording medium type determining device; a tiltangle adjuster for adjusting said tilt angle; and a driver for drivingsaid tilt angle adjuster in accordance with said tilt drive signal.
 2. Atilt servo control device according to claim 1, wherein said tilt angleadjuster includes a liquid crystal panel having a plurality of regionsarranged in said optical system, and said driver drives each of saidplurality of regions of said liquid crystal panel in accordance withsaid tilt drive signal.
 3. A tilt servo control device according toclaim 1, wherein said recording medium type determining devicedetermines which optical disk of at least a CD-ROM, a CD-R, asingle-layered DVD-ROM, a double-layered DVD-ROM, a DVD-RW, a generalpurpose DVD-R, an authoring purpose DVD-R and a DVD-RAM is set as saidoptical recording medium into said apparatus at the time of recordinginformation.
 4. A tilt servo control device according to claim 1,wherein said recording medium type determining device determines whichoptical disk of a CD type disk including a CD-ROM and a CD-R, and a DVDtype disk including a DVD-ROM, a DVD-RW, a DVD-R, and a DVD-RAM is setas said optical recording medium into said apparatus at the time ofreproducing information.
 5. A tilt servo control device according toclaim 1, wherein said recording medium type determining device includesa continuous focus driver for driving an focus actuator for adjusting afocal position on said optical recording medium so as to move the focalposition continuously at a constant speed; a device for observing anS-characteristic produced in a focus error signal obtained from a focuserror signal generating circuit during the drive operation of saidcontinuous focus driver; and a first type determining device fordetermining a type of said optical recording medium in accordance with atime interval between appearances of the S-characteristic.
 6. A tiltservo control device according to claim 5, wherein said first typedetermining device determines that said optical recording medium is a CDtype disk including a CD-ROM and a CD-R when said time interval betweenappearances of said S-characteristic is larger than a time thresholdvalue and determines that said optical recording medium is a DVD typedisk including a DVD-ROM, a DVD-RW, a DVD-R and a DVD-RAM when said timeinterval between appearances of said S-characteristic is smaller thanthe time threshold value.
 7. A tilt servo control device according toclaim 5, wherein said recording medium type determining device furtherincludes a second type determining device for determining a type of saidoptical recording medium in accordance with the amplitude of saidS-characteristic.
 8. A tilt servo control device according to claim 7,wherein said second type determining device determines that said opticalrecording medium is a first category disk including a single-layeredDVD-ROM and a DVD-R when the amplitude of said S-characteristic islarger than an amplitude threshold value and determines that saidoptical recording medium is a second category disk including adouble-layered DVD-ROM, a DVD-RW and a DVD-RAM when the amplitude ofsaid S-characteristic is smaller than the amplitude value.
 9. A tiltservo control device according to claim 5, wherein said recording mediumtype determining device further includes a third type determining devicefor determining a type of said optical recording medium by detectingwhether said read signal or a tracking error signal obtained from atracking error signal generating circuit contains a groove wobblecomponent signal or not.
 10. A tilt servo control device according toclaim 9, wherein said third recording medium type determining devicedetermines that said optical recording medium is a DVD-R when the groovewobble component signal is contained and determines that said opticalrecording medium is a single-layered DVD-ROM when the groove wobblecomponent signal is not contained.
 11. A tilt servo control deviceaccording to claim 9, wherein said third recording medium typedetermining device determines that said optical recording medium is aDVD-RW or a DVD-RAM when the groove wobble component signal is containedand determines that said optical recording medium is a double-layeredDVD-ROM when the groove wobble component signal is not contained.
 12. Atilt servo control device according to claim 5, wherein said recordingmedium type determining device further includes a fourth typedetermining device for determining a type of said optical recordingmedium in accordance with the contents of land pre-pit information ofsaid optical recording medium obtained from said read signal.
 13. A tiltservo control device according to claim 12, wherein said fourthrecording medium type determining device determines that said opticalrecording medium is a general purpose DVD-R or an authoring purposeDVD-R in accordance with the contents of the land pre-pit information ofsaid optical recording medium.
 14. A tilt servo control device accordingto claim 5, wherein said recording medium type determining devicefurther includes a fifth type determining device for determining a typeof said optical recording medium in accordance with existence ornon-existence of a land pre-pit on said optical recording medium.
 15. Atilt servo control device according to claim 14, wherein said fifthrecording medium type determining device determines that said opticalrecording medium is a DVD-RW when a land pre-pit exists and determinesthat said optical recording medium is a DVD-RAM when no land pre-pitexists.
 16. A tilt servo control device according to claim 14, whereinsaid fifth recording medium type determining device determines that saidoptical recording medium is a DVD type disk other than a DVD-RAM when aland pre-pit exists and determines that said optical recording medium isa DVD-RAM when no land pre-pit exists.
 17. A tilt servo control deviceaccording to claim 2, wherein said tilt drive signal generator includes:a first tilt servo section having a push-pull component generator forgenerating a push-pull component signal containing differentialcomponents of output signals of respective split portions of said photodetector, a first tilt error signal generator for generating a firsttilt error signal representing the tilt angle based on said push-pullcomponent signal and a generator for generating a signal representing acorrection value for each of said plurality of regions in response tosaid first tilt error signal; a second tilt servo section having a delayelement for delaying said read signal by a predetermined time period, asecond tilt error signal generator for generating a second tilt signalby subtracting said read signal from an output signal of said delayelement and a generator for generating a signal representing thecorrection value for each of said plurality of regions in response tosaid second tilt error signal; a third tilt servo section for generatinga signal representing the correction value for each of said plurality ofregions so as to maximize the level of said read signal; a selector forselecting one tilt servo section of said first, second and third tiltservo sections in accordance with the type of the recording mediumdetermined by said recording medium type determining device; and agenerator for generating said tilt drive signal in accordance with thecorrection value output from the one tilt servo section selected by saidselector.
 18. A tilt servo control device according to claim 17, whereinsaid selector selects said first tilt servo section when said recordingmedium type determining device determines that said optical recordingmedium set into said apparatus at the time of recording information is aDVD-RW or a general purpose DVD-R, and selects said second tilt servosection when said recording medium type determining device determinesthat said optical recording medium set into said apparatus at the timeof recording information is a DVD-RAM.
 19. A tilt servo control deviceaccording to claim 17, wherein said selector selects said second tiltservo section when said recording medium type determining devicedetermines that said optical recording medium set into said apparatus atthe time of reproducing information is a DVD-RAM, and selects said thirdtilt servo section when said recording medium type determining devicedetermines that said optical recording medium set into said apparatus atthe time of reproducing information is a DVD type disk other than aDVD-RAM.
 20. A tilt servo control device according to claim 1, whereinthe tilt adjusting operation of said tilt angle adjuster is stopped whensaid recording medium type determining device determines that saidoptical recording medium set into said apparatus at the time ofrecording or reproducing information is a CD type disk.
 21. A tilt servocontrol device according to claim 17, wherein said predetermined timeperiod corresponds to time taken when the irradiating position of thelaser beam moves a first header field and a second header field of aheader section of a DVD-RAM.
 22. A tilt servo control method of aninformation recording/reproducing apparatus for recording information onand reproducing information from an optical recording medium set intosaid apparatus, said apparatus comprising an optical system for leadinga laser beam emitted from a light source to a recording surface of theoptical recording medium and a laser beam reflected by the recordingsurface of the recording medium to a photo detector and a read signalgenerator for generating a read signal in accordance with an outputsignal of the photo detector, said method comprising the steps of:determining a type of said optical recording medium; generating a tiltdrive signal so as to reduce a tilt angle between a normal to therecording surface of said optical recording medium at a position of saidlaser beam irradiating said recording surface and an optical axis ofsaid laser beam by a method for generating a tilt drive signalcorresponding to the recording medium type; and driving a tilt angleadjuster for adjusting said tilt angle in accordance with said tiltdrive signal.